Synthesis, structure, and magnetic properties of Co, Ni, and Co-Ni alloy nanocluster-doped SiO2 films by sol-gel processing

The optical, structural, and magnetic properties of Co, Ni, and CoxNi100-x (0 < x < 100) alloy nanoclusters in silica host obtained by the sol-gel route are presented. Throughout the entire range of composition investigated, from pure Ni to pure Co, the nanoclusters exhibit an fcc structure, with lattice parameters increasing with the Co fraction in the system. This indicates Co-Ni alloy formation. It has also been observed that the average cluster diameter increases with increasing Co fraction in the system. An enhancement of the magnetic moment was exhibited in the pure Co and Ni samples, and good agreement between the measured values and those of the corresponding bulk alloys was found for the other samples. All composites are superparamagnetic at room temperature.